NONE.
1. Field of the Invention
The present invention relates to devices and methods for preventing an unintended or premature activation of one or more downhole tools.
2. Description of the Related Art
One of the activities associated with the completion of an oil or gas well is the perforation of a well casing. During this procedure, perforations, such as passages or holes, are formed in the casing of the well to enable fluid communication between the well bore and the hydrocarbon producing formation that is intersected by the well. These perforations are usually made with a perforating gun loaded with shaped charges. The gun is lowered into the wellbore on electric wireline, slickline or coiled tubing, or other means until it is adjacent the hydrocarbon producing formation. Thereafter, a surface signal actuates a firing head associated with the perforating gun, which then detonates the shaped charges. Projectiles or jets formed by the explosion of the shaped charges penetrate the casing to thereby allow formation fluids to flow from the formation through the perforations and into the production string for flowing to the surface.
A number of arrangements can be used to actuate the firing head. For example, the firing head may be actuated by dropping a weight onto the firing head through tubing extending from the firing head to a wellhead or a platform at the earth""s surface. The falling weight eventually strikes a firing pin in the firing head, thereby actuating a detonator explosively coupled to the perforating gun. Other tubing conveyed perforating systems employ a differential firing head that is actuated by creating a pressure differential across an actuating piston in the firing head. The pressure differential is created by applying increased pressure either through the tubing string or through the annulus surrounding the tubing string to move the actuating piston in the firing head. Typically, the firing head actuating piston will have hydrostatic pressure applied across the actuating piston as the tool is run into the well. When it is desired to operate the tool, the increase in pressure is sufficiently large to initiate detonation of the firing head and perforating gun. Often, perforating guns have been actuated electrically. The firing head and perforating gun are lowered into the well on a wireline. Electrical current is sent through the wireline to set off the firing head. The firing head in turn detonates the shaped changes in the perforating gun.
Regardless of the system used, it is desirable to ensure that the charges do not detonate prematurely. Premature detonation can be of particular concern when the perforating gun is on the surface; i.e., not within the confines of a well bore. For example, electrically actuated explosive device can be susceptible to detonation by stray electrical signals, radio signals picked up by the conductive wireline, static electricity or lightning strikes. Any electrical noise or discharges from any of these sources can cause the device to explode prematurely with the risk of damage to the production system and danger to operators on the oil production installation. Mishandling during transportation or during manual deployment may also inadvertently actuate mechanically actuated systems. Accordingly, a number of devices have been developed to prevent the premature detonation of charges carried by a perforating gun.
In an exemplary conventional safety system, a safety module associated with the perforating gun has a housing, a pressure sensitive switch and a temperature sensitive switch. The switches only allow an electrical command signal to be conveyed to the tool when the pressure and temperature both reach predetermined pressure and temperature values. In another exemplary safety system, applying fluid pressure to the exterior of a housing arms an electrical firing system. The firing system arms when the fluid pressure exceeds the well hydrostatic pressure. The firing system is controlled by a microprocessor that is preset to be responsive only to a selected value of fluid pressure surrounding the control housing. These systems depend, in part, on a reliable prediction of well bore conditions. If the temperature or pressure of the well bore at the desired depth does not match the pre-set values, then the gun will not arm. In these instances, the gun will have to tripped up and the safety module reset. It will be appreciated that this additional procedure lead to lost time and additional expenditures of effort and money.
Perforating guns are, however, only one example of downhole tools that require the use of safety mechanisms that control activation. Other tools, such as pipe cutters, use caustic acid to burn and sever a section of pipe. While the closed wellbore environment enables these downhole tools to operate safely, a common characteristic of these downhole tools is that unintended surface activation can cause injury to personnel and damage to nearby equipment.
The present invention addresses these and other drawbacks of the prior art.
The present invention provides devices and systems for controlling the activation of one or more downhole tools. In one aspect, the system prevents an unintended or premature activation of one or more downhole tools activated by an initiation device. A preferred system is configured to allow an initiation signal generated by a signal generator or source to reach the initiation device only after the downhole tool has reached a known pre-determined depth at a location that is substantially stationary relative to the earth""s surface. The preferred safety system includes a first device associated with the downhole tool and a second device fixed at the stationary location. The first device is configured to permit an initiation signal transmitted by the generator to reach the initiation device upon reaching the stationary location (xe2x80x9csignal pass-throughxe2x80x9d). The second device positively engages the first device to provide a positive indication that the specified depth has been reached. In another preferred embodiment, the system includes a bypass, a switch, and a trigger. The bypass is operably coupled to a signal conveyance medium connecting the generator to the initiation device. The bypass has a safe mode in during which it prevents signal pass-through and a fire ready mode during which it allows signal pass through. The switch is mechanically connected to the bypass and can move the bypass between the two modes. The trigger, however, is positioned at the relatively stationary location (e.g., in the wellhead or wellbore) and is configured to positively engage the switch. The trigger may be a rigid member, a biased member, or utilize hydraulic power. While at the surface, the bypass is by default set in the safe mode. During tool deployment, the switch engages the trigger during transit through a wellhead or well bore. This engagement may, for example, be facilitated by the cooperative action of alignment pins and channels. Engagement between the trigger and the switch causes the bypass to move from the safe mode to a fire ready mode. In a preferred embodiment, engagement between the trigger and the switch during tool extraction causes the bypass to move from a fire ready mode to a safe mode.
In a different aspect, a preferred safety system prevents an energy train generated by an initiation device from reaching the downhole tool until the downhole tool has reached a known depth in a well. The preferred safety mechanism includes a first device associated with the downhole tool and a second device fixed at a stationary location. The first device is configured to permit the energy stream to reach the downhole tool if the tool is below a specified depth below the earth""s surface (xe2x80x9cenergy pass-throughxe2x80x9d). The second device positively engages the first device to provide an indication that the pre-defined or specified depth has been reached. In one preferred embodiment, the safety system includes a bypass, a switch, and a trigger. The bypass is operably coupled to a energy conveyance conduit connecting the initiation device to the downhole tool. The bypass has a safe mode in during which it prevents energy pass-through and a fire ready mode during which it allows energy pass through. The switch is mechanically connected to the bypass and can move the bypass between the two modes. The trigger, however, is positioned at the relatively stationary location (e.g., in the wellhead or wellbore) and is configured to positively engage the switch. The components operate in substantially the same way as previously described.
In related embodiments, trigger may include one or hydraulically actuated members such as finger or rams. The member can be configured to actuate the switch using a pre-defined movement (e.g., linear motion, rotation, and pivoting). Additionally, the preferred system can include a mode indicator operably connected to said trigger that provides an indication of whether the bypass can pass the initiation signal to the initiation device. Moreover, the trigger can include a biasing member for urging said trigger against said switch and/or maintaining the trigger in a predetermined position. Devices such as channels formed in a housing and/or pins can be used to guide the trigger to the switch. In one preferred embodiment, the system includes two triggers: a first trigger that causes the bypass to move from a safe mode to a fire ready mode, and a second trigger that causes the bypass to move from the fire ready mode to a safe mode. In another preferred embodiment, a housing enclosing the bypass includes a first section rotatably coupled to a second section. The bypass prevents signal pass-through when said first and second sections have a first relative angular alignment and permits signal pass-through when the first and second sections have a second relative angular alignment. Hydraulically actuated rams associated with the trigger are adapted to selectively move the first and second sections between the first and second relative angular alignments.
In another embodiment, the bypass is housed in a housing having an external sleeve member. The sleeve slides between a first position wherein the bypass permits signal pass-through and a second position wherein the bypass prevents signal pass-through. A trigger blocks sleeve movement in a pre-defined direction when extended. Force applied to the housing in a direction opposite to the pre-defined direction causes relative movement between the sleeve and the housing. This relative movement is used to shift the sleeve between the first and second positions.
Downhole tools that can be used with embodiments of the present invention include perforating guns, pipe cutters, and other tools that release a relatively substantial amount of energy when activated.
It should be understood that examples of the more important features of the invention have been summarized rather broadly in order that detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto.